An electric double layer capacitor is capable of being configured in small size and light weight, having a high energy density, and being charged and discharged repeatedly. Taking advantage of its properties, the demand for electric double layer capacitor is rapidly increasing. Since the electric double layer capacitor can be charged and discharged rapidly, the capacitor is utilized as a small size power supply for memory backup in personal computers. In recent years, its application to a large size power supply for electric automobiles is expected for overcoming environmental problems and resource problems. With such an expansion of usage and growth, there is a demand for further improving the properties of the electric double layer capacitor, e.g., reduction of the internal resistance, increase of the electrostatic capacity and enhancement of mechanical property.
In order to enhance these properties, various improvements are being made as to materials for forming the active material layer on the current collector (in the present invention, such a material is referred to as an electrode material for the electric double layer capacitor or simply an electrode material). The electrode material for the electric double layer capacitor contains an electrode active material such as activated carbon as a major component, and optionally contains conductive materials and binders for imparting functions such as conductivity, cohesiveness and flexibility to the electrode. However, these components other than the electrode active material may cause reduction of electrode properties, e.g., the increase of resistance in the electrode and the reduction of a capacitor capacity.
In Patent document 1, it is disclosed that the electrode material for the electric double layer capacitor is obtainable by dispersing in water powders obtained by pulverizing activated carbon fibers as an electrode active material, mixing the dispersion with latex of chlorosulfonated polyethylene as a binder, subsequently removing the water and pulverizing/granulating a resulting solid.
Patent document 2 discloses a composite particle (corresponding to the mixture particle in the present invention) comprising an electrode active material, a conducting auxiliary agent and a binder, obtained by a fluidized bed granulation method, where the conducting auxiliary agent and the binder have been cohered and integrated.
Patent Document 1: JP Sho-62-179711 A
Patent Document 2: JP 2005-26191 A